Funnel Cloud in Oregon, December 1, 2018

Area Forecast Discussion
National Weather Service Portland OR
921 AM PST Sat Dec 1 2018

.SYNOPSIS...Upper low off the north Oregon coast will slowly track
southeastward today, maintaining cool, showery weather. Snow levels
will remain below the Cascade passes with some additional
accumulation expected. Showers then decrease by tonight through
Sunday. Storm track stays well south of the region this coming week,
with high pressure building over the Pacific NW. This will bring cool
and dry weather for most of the upcoming week, with East Winds
developing Sunday night and Monday.
&&

.SHORT TERM...Today through Monday...Water vapor imagery shows the
upper low just west of Tillamook at this time. It will continue to
track south/southeastward today. As it does, the flow at and below
700 mb maintains an upslope component for the Cascades and Coast
Range. This weak upslope combined with steep lapse rates, diurnal
surface heating, and cool temperatures aloft are sufficient to
maintain scattered rain and snow showers (above 2000-2500 feet) in
the forecast through the afternoon. No forecast updates at this time
and the remainder of the AFD is unchanged. Bright

Will maintain winter weather advisory for Oregon Cascades today.
But, will end the advisory for the south Washington Cascades, where
probably only get another 1 to 4 inches for that area, as showers
will be decreasing earlier in the day.

Showers decreasing tonight, especially over north of a Newport to
Salem to Mt Hood line. Though will be cooler, with many valleys
falling into the lower to middle 30s later tonight. This may lead to
some patchy icy spots, mainly in rural areas where lingering moisture
on roads/bridges may freeze.

Models continue to show showers decreasing on Sunday, with PoPs
generally 20 to 40 pct, and with that the higher PoPs will be over
Lane County. Otherwise, cool day with a mix of sunshine and clouds.

Skies clearing later Sunday night, with cooler temperatures. Good bet
will see overnight lows dropping into the middle to upper 20s, with
areas of fog forming. Will see higher potential for icy spots late
Sun night into Mon am, thanks to areas of freezing fog. Motorists
will have to keep that in mind for travel at that time.

Now, upper low will be well south/east of the region by Mon am, with
high pressure building over the Pac NW. This high will bring dry
conditions, with areas of fog persisting into midday. But the
building high will also start to increasing offshore flow, with east
winds developing later Mon afternoon.			   Rockey.

.LONG TERM...Monday night through Friday. Much of the extended
period of the forecast looks to remain dry as an upper level low
slides south and eventually into California early next week. This
results in weak upper level ridging across the forecast area, with a
dry offshore lower-level flow developing. In this pattern,
temperatures will trend several degrees below normal. As a result,
expect several nights with overnight temperatures dropping into the
20s through the Willamette Valley and the lower to mid 30s along the
coast. Meanwhile, increasing offshore flow could lead to some gusty
and cold east winds through the Columbia River Gorge and far east
Portland metro area for much of the midweek period. The next front,
and renewed precipitation chances, return by late Friday as the
upper level ridge breaks down and slides to the east, opening the
door for the next disturbance to approach the forecast area. Cullen

&&

.AVIATION...A low pressure system continues to move onshore on
the central OR coast through the afternoon. This will drive
continued showers, and potentially even a few isolated
thunderstorms. Expect a mix of VFR and MVFR during this time.
The shower threat shifts to the southern half of the CWA, from
around KSLE south, by late morning with potential for periodic
MVFR conditions to carry into the afternoon. Expect conditions to
improve to mostly VFR north of KSLE by around 18Z. There will be
a slight chance for thunderstorms around today, with the best
chances over the waters.

PDX AND APPROACHES...A mix of VFR and MVFR conditions this
morning in showers. Showers chances decrease through the day,
with predominantly VFR conditions expected after 18z. Slight
chance of showers continues through the afternoon. Pyle/42

&&

.MARINE...A low pressure system centered just west of the mouth
of the Columbia River will gradually push SE through the waters
during the afternoon. There will be a slight chance for
thunderstorms out ahead of the low. As the system makes land
fall expect the southwesterly winds to turn northwesterly over
the waters. The wind shift will be from north to south as the
low moves through. 20 to 25 kt gusts are modeled to continue over
the far outer waters, generally 40 nm and out, through tonight,
so will hang on to a small craft advisory for winds for
PZZ270/PZZ275. Offshore flow is expected to build over the waters
late Sun into Mon and will likely last through much of next
week. The offshore winds may become gusty enough to require small
craft advisories at times next week.

Seas will remain around 10 to 12 feet with a dominant period of
11 to 12 seconds through tonight. Seas start to subside late
Saturday night/Sunday morning, falling below 10 ft by midday
Sunday. Seas should then remain below 10 ft through much of next
week. Pyle/42

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory until 6 PM PST this evening for
     Cascades in Lane County-Northern Oregon Cascades.

WA...None.
PZ...Small Craft Advisory for hazardous seas until 7 AM PST Sunday
     for Coastal Waters from Cape Shoalwater WA to Florence OR
     out 60 NM.

     Small Craft Advisory for winds until 1 AM PST Sunday for Waters
     from Cape Shoalwater WA to Florence OR from 10 to 60 NM.

     Small Craft Advisory for Rough Columbia River Bar until 3 PM
     PST this afternoon.

     Small Craft Advisory for Rough Columbia River Bar from 10 PM
     this evening to 3 AM PST Sunday.

&&

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This discussion is for Northwest Oregon and Southwest Washington
from the Cascade crest to 60 nautical miles offshore. This area is
commonly referred to as the forecast area.